Plastic molding offers numerous benefits in the production of simple products. Many plastic molded products have high functionality and quality, and a low cost to manufacture. In addition, plastic molding allows high volume production of essentially identical products with consistent quality. This is especially true with products having simple geometric configurations, allowing the use of a two-part mold. In a typical two-part mold, the mold has two halves that join together to define a void, with the void having the same shape as the product to be molded. During molding, the void is filled with plastic to form the product. The mold halves then separate linearly from one another to remove the part from the mold. The complexity of the part molded in a two-part mold is obviously limited by the fact that the mold splits into two halves that move linearly with respect to each other. More complexly shaped products require molds with additional movable portions, or with additional sections that split apart or move relative to one another. This significantly increases the cost and complexity of the mold, and consequently increases the cost of the product molded. Therefore, it is strongly preferred that plastic molded products be designed such that a simple mold may be used. It is especially preferred that a two-part mold be used to form the part.
A number of traditionally non-plastic products have been successfully replicated in plastic. Examples include plastic deck boards, fence posts, latticework, porch columns and railings. Plastics have not been successfully used to form large structural or truss work panels. This is partially due to the complexity and size of such a product, and also to the need to minimize the use of plastic. The cost of plastic products is typically directly proportional to the volume of plastic used to form the part. Therefore, cost minimization requires minimization of plastic.
Truss work panels have wide applicability, including use as structural reinforcement members in wall panels and building materials. However, typical truss work panels have a complicated design that make it impossible to integrally form the truss work. Instead, the truss work is typically assembled from a multiple of pieces, which is time and labor intensive. U.S. Pat. No. 6,076,324 to Daily et al. shows a truss structure design that is integrally formed using stereolithography or other rapid prototyping techniques to integrally form the three-dimensional truss structures or to create disposable molds. While offering some benefits, the Daily design remains complicated to manufacture, and would be impossible to form using traditional two-part injection molding.
U.S. Pat. Nos. 4,180,232; 4,419,321; and 4,757,665, each to Hardigg, disclose a truss panel that can be molded using traditional two-part molds. However, the Hardigg design lacks any members that extend directly perpendicularly between members in an upper and lower set. This compromises the ability of the truss work to withstand structural loads.